The present invention relates to a smooth vent valve that supplies an inert gas into a vacuum chamber of a semiconductor manufacturing system or the like to return the pressure in the vacuum chamber from a vacuum to the atmospheric pressure in such a manner that dust attached to the floor and wall surfaces of the vacuum chamber and piping will not be whirled up by the inert gas.
Vacuum chambers of semiconductor manufacturing systems or the like include a vacuum treating chamber and a load-lock chamber (i.e. a chamber placed between a vacuum treating chamber and an atmospheric chamber). To unload wafers, for example, from the load-lock chamber into the atmospheric air, an inert gas, e.g. nitrogen gas, is supplied into the vacuum chamber (load-lock chamber), which is under vacuum, to destroy the vacuum. At this time, dust (dust particles) attached to the floor and wall surfaces of the vacuum chamber and piping may be whirled up by the injected gas and suspended in the chamber. The suspended dust particles are likely to adhere to wafers, producing an adverse effect on the performance of semiconductors. Dust is not particularly harmful if it remains attached to the floor or wall surface. Accordingly, it is common practice to use an apparatus that gradually increases the flow rate of the injected gas in order to avoid suspension of dust particles when the vacuum is destroyed.
FIG. 6 shows a conventional apparatus [for example, see Japanese Patent Application Unexamined Publication (KOKAI) No. 2-229983]. A gas container 1 and a vacuum chamber 10 are communicated with each other by a main passage 2 and a sub-passage 3. The main passage 2 is provided with a main valve 5. The sub-passage 3 is provided with a sub-valve 6 and a flow control valve 7, which are placed in series. At an initial stage of gas supply, the gas is supplied slowly so as not to whirl up dust by opening the sub-valve 6 and lowering the flow rate through the flow control valve 7. The main gas supply is carried out by opening the main valve 5 when the pressure in the vacuum chamber 10 has approached the atmospheric pressure to a certain extent. Thus, no dust is whirled up even if the gas is supplied at a high flow rate. Accordingly, the pressure in the vacuum chamber 10 can be raised to the atmospheric pressure within a short period of time. However, the conventional apparatus has the disadvantages that the piping becomes complicated and requires an increased space, and that the number of parts increases, resulting in an increase in the cost, and further that a leakage test must be carried out for each joint.
An L-shaped valve for vacuum apparatus, in which a main valve, a sub-valve and a flow control valve are integrated into one unit, is known as a device to be provided in an exhaust flow path for a vacuum chamber [for example, see Japanese Utility Model Application Unexamined Publication (KOKAI) No. 3-6175]. In the conventional L-shaped valve for vacuum apparatus, an annular main valve seat is placed in a flow path between an inlet and outlet ports of a valve body, and a disk-shaped main valve element is provided at a position opposite to the main valve seat. The main valve element has an orifice extending therethrough. An approximately disk-shaped auxiliary valve element is provided at the upper end of the main valve element to face opposite to the orifice. The main valve (on-off valve), which consists essentially of the main valve element and the main valve seat, is opened by separating the main valve element from the main valve seat. The main valve is closed by bringing the main valve element into contact with the main valve seat. When the main valve is closed and the auxiliary valve element is separate from the main valve element, the fluid flows through the orifice in the main valve element. When the main valve is closed and the auxiliary valve element is placed in contact with the main valve element, the orifice is also closed. The conventional L-shaped valve for vacuum apparatus is operated by actuating a handle. Therefore, the L-shaped valve is not easy to operate and incapable of controlling the flow rate of the fluid flowing through the orifice.